1. Field of the Invention
This invention relates to a steering control system for a vehicle.
2. Description of the Related Art
Earlier patent applications proposed by the assignee, including those made public by Japanese Laid-Open Patent Application Nos. Hei 5(1993)-197,423 and Hei 9(1997)-221,054, teach vehicle steering control system technologies that provide steering angle assistance for keeping the vehicle on a desired course of travel along a lane of a road.
By providing fine steering assistance while preventing vehicle lane wandering, these technologies greatly reduce the burden on the driver, which tends to increase particularly during long, high-speed driving on an expressway or the like.
In view of the interference or interaction between this type of steering assistance control and driver steering, the control should preferably be effected to provide assistance through torque (steering force) rather than steering angle.
Aside from the above, it is desirable to detect or discriminate whether a failure has occurred in such a torque assist system with accuracy and take an appropriate countermeasure to cope with the failure condition.